Semiconductor device

1. A semiconductor device comprising: an internal circuit which is arranged on a chip and is operated at any of a first dropped voltage and a second dropped voltage; a main voltage dropping circuit, arranged on the chip, for dropping a first input voltage to the first dropped voltage and outputting the first dropped voltage to the internal circuit; a secondary voltage dropping circuit, arranged on the chip and having a current supplying capability and an electric power consumption rate smaller than those of the main voltage dropping circuit, for dropping the first input voltage or second input voltage to the second dropped voltage and outputting the second dropped voltage to the internal circuit; a first power supply terminal which is arranged on the chip so as to allow connection with a first external voltage source having the first input voltage and is connected with the main voltage dropping circuit; and a second power supply terminal which is arranged on the chip so as to allow connection with either the first external voltage source or a second external voltage source having the second input voltage and is connected with the secondary voltage dropping circuit.

2. A semiconductor device according to claim 1 , further comprising switching means, which is arranged in a wire extending from the first power supply terminal to the first external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the first external voltage source through the first power supply terminal.

3. A semiconductor device comprising: a main voltage dropping circuit, arranged on a chip, for dropping a first input voltage to a first dropped voltage and outputting the first dropped voltage; a secondary voltage dropping circuit, arranged on the chip and having a current supplying capability and an electric power consumption rate smaller than those of the main voltage dropping circuit, for dropping the first input voltage or a second input voltage to a second dropped voltage and outputting the second dropped voltage; a first circuit unit of an internal circuit which is connected with the main voltage dropping circuit on the chip and is operated in cooperation with the main voltage dropping circuit; a second circuit unit of the internal circuit which is arranged on the chip and is operated in any time including a low electric power consumption time; first switching means, arranged on the chip, for selecting either a connection between the second circuit unit and the main voltage dropping circuit and a connection between the second circuit unit and the secondary voltage dropping circuit; a first power supply terminal which is arranged on the chip so as to allow connection with an external voltage source and is connected with the main voltage dropping circuit; and a second power supply terminal which is arranged on the chip so as to allow connection with the external voltage source and is connected with the secondary voltage dropping circuit.

4. A semiconductor device according to claim 3 , further comprising second switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal; and a signal line through which a switching control signal is directly or indirectly sent to both the first switching means and the second switching means.

5. A semiconductor device according to claim 3 , further comprising: second switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal; a signal line through which a switching control signal is sent to the second switching means; voltage comparing means for monitoring a voltage applied to the first power supply terminal, comparing the voltage and a prescribed threshold voltage and outputting a signal indicating a compared result; and control means, connected with the voltage comparing means, for controlling a selection operation performed by the first switching means according to the signal output from the voltage comparing means.

6. A semiconductor device according to claim 3 , further comprising: second switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal; and voltage supply form determining means for determining a voltage supply form according to an operation state of the internal circuit and outputting a switching control signal directly or indirectly to both the first switching means and the second switching means to supply the first dropped voltage or the second dropped voltage corresponding to the voltage supply form to the internal circuit.